|  | 1.6 | The Transport Layer of the OSI Reference Model
| 1.6.5 | Windowing
In the most basic form of reliable connection-oriented data transfer, data packets must be delivered to the recipient in the same order in which they were transmitted. The protocol fails if any data packets are lost, damaged, duplicated, or received in a different order. The basic solution is to have a recipient acknowledge the receipt of every data segment. If the sender has to wait for an acknowledgment after sending each segment, throughput is low. Because time is available after the sender finishes transmitting the data packet and before the sender finishes processing any received acknowledgment, the interval is used for transmitting more data. The number of data packets the sender is allowed to have outstanding without yet receiving an acknowledgment is known as the window. Windowing is a method to control the amount of information transferred end-to-end. Some protocols measure information in terms of the number of packets; TCP/IP measures information in terms of the number of bytes.